Italian police have opened an investigation for doping against Jamaican sprinters Asafa Powell and Sherone Simpson, police said on Tuesday, as the athletes blamed their physiotherapist after they failed drugs tests.

The pair, who tested positive for a banned stimulant, were training in northeast Italy but have now left the country after a police raid on their hotel, a local police officer said.

Canadian physiotherapist Chris Xuereb, who is similarly under investigation, has also left Italy, the officer, who declined to be identified, added.

The prosecutor's office in Udine, the city closest to where the Jamaican team was staying, is leading the investigation for suspected violation of a law that punishes the supply and ingestion of stimulants.

Prosecutors have also confirmed the seizure of around 50 boxes including creams, sprays and vials that were seized in a search of the rooms of Powell, Simpson and Xuereb in the night between Sunday and Monday.

Police and prosecutors are currently looking for a laboratory that can carry out tests.

"All we know is that they (Powell, Simpson and Xuereb) have left Lignano," the officer said. "The substances we seized still have to be tested.

"We began the investigation because of the positive test results that were announced. We are not planning to conduct our own (doping) tests (on the athletes)."

Athletes say food supplements behind positive test results

The development came after both athletes pointed to contaminated food supplements as the reason why they failed the dope tests, which have cast a cloud over the build-up to the athletics world championships in Moscow next month and put sprinting in the spotlight.

Britain's Daily Telegraph quoted Paul Doyle as saying in an interview that both Powell and Simpson had only recently begun working with Xuereb.

US-based Doyle said he had no reason to suspect "mal-intent" on Xuereb's part and that, like the athletes, he was probably unaware of exactly what the supplements contained.

Both athletes tested positive for oxilofrine at the Jamaican championships last month.

Italian police reportedly brought Xuereb in for questioning and raided his base on Monday, although ANSA said no arrest had been made.

"Asafa and Sherone have been working with WADA (the World Anti-Doping Agency) to arrange this police raid, so to speak," Doyle was quoted as saying.

"Once we knew of the positive test, we realised that Asafa and Sherone were the only two athletes in the group who had been given new supplements by this phsyio that they are working with.

"Asafa's had probably 150 to 200 clear tests in the past. He starts working with a new physio who gives him new supplements and all of a sudden he has a positive test in his first test.

"It's obvious there's no other reason why he would have tested positive other than something being in the new supplements he's been taking.

"So we immediately asked WADA to get the police there to go in and search everything in the physio's possession as well as everything in Asafa and Sherone's possession."

Xuereb began treating Powell for a hamstring injury that flared up in March this year, according to Doyle.

He added that Xuereb gave Powell 17 supplements, three of which were administered by injection, and all were legal, he added.

Simpson checked whether any of the supplements contained proscribed substances, although did not seek independent medical verification, Doyle said.

He also accepted that Powell had not informed his coach, Stephen Francis, about the supplements.

Powell, a 4x100m relay gold medallist at the 2008 Olympics in Beijing, is one of the four fastest men over 100m in history.

News of his positive test emerged on Sunday with a separate positive test for US sprinter Tyson Gay.

Simpson won gold for Jamaica in the 4x100m relay at the Athens Olympics in 2004 and silver in the event last year in London. She also won 100m silver in Beijing.